residential heat pump water heaters: hvac interaction study rtf hpwh subcommittee may 14, 2015
TRANSCRIPT
Residential Heat Pump Water Heaters:HVAC Interaction Study
RTF HPWH SubcommitteeMay 14, 2015
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Today’s Agenda
• Brief recap and context for today’s meeting• Present and discuss key questions• Work towards subcommittee recommendation on both questions
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Introduction
• November 2014, RTF directed staff to develop a research plan to study the HVAC interaction effect induced by heat pump water heaters (HPWHs)
• April 2015, RTF accepted a research strategy for studying the HVAC interaction (or thermal coupling) parameter
• NEEA has agreed to sponsor and fund (or co-fund) this research, but has asked the RTF subcommittee to weigh in on some of the final technical details of the PNNL Lab Homes study
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Sensitivity of Total HPWH Savings to HVAC Interaction Factor
HZ1 HZ2 HZ3 HZ1 HZ2 HZ3 HZ1 HZ2 HZ3Zonal Electric Resistance Electric Furnace Heat Pump
-
200
400
600
800
1,000
1,200
1,400
1,600
Tier 1, Interior
50%
75%
100%
Tota
l Ene
rgy
Savi
ngs (
Hot W
ater
+ H
eatin
g), k
Wh
Interaction Factor
+/- ~20%
Research Strategy: PNNL Lab Homes(from April 2015 RTF meeting)
• Research Goal– Observe the space conditioning energy interaction that results from the
installation of a HPWH in interior spaces
• Data Collection– PNNL Lab Home Study: Test four install locations throughout home
• Use 1kW space heaters and operate on a schedule similar to HPWHs• 5-10 days per location
• Analysis– Compute change in space heating requirement and HVAC interaction factor
for each location– Observe range of results; depending on range, results may be combined
(averaged) if within a narrow band, or results could point to needing additional measure identifiers
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Key Questions for Today
1. What equipment should be used to induce the localized temperature change in the experiment home?
2. What locations and conditions should be tested in the experimental home?
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Question 1
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Equipment to Induce Temp EffectWhat equipment should be used to induce the localized temperature change in the experiment home?
Space Heater Portable A/C Unit HPWH
Uncertainty of Equipment Output/Performance Low High High
Cost to Setup and Run Experiment Low Medium High
Ability to Add Cooling Gain to Space (i.e. similar to that of a HPWH) No Somewhat Yes
Ability to Simulate the Magnitude of a HPWH's HVAC Interaction Effect Yes* Yes Yes
* If we can show experimental setup where heating gain produces symmetric HVAC interaction (i.e. as compared to cooling gain)
Equipment Used to Test HVAC Interaction / Thermal Coupling Effect
Equipment Characteristic
Space Heater Portable A/C Unit HPWH
Uncertainty of Equipment Output/Performance Low High High
9 Definition: Thermal Utility• Thermal Utility
– Tells you if “waste heat” is useful or not– The ratio of useful internal heat gains to total gains that offset a heating requirement– Example:
• Heating is required in a house for 6 months of the year • Internal gains are 2,000 kWh/yr Useful gains are 1,000 kWh/yr. Thermal utility is 0.5.
J F M A M J J A S O N D
Heating Energy Required
Energy from Internal Gains Gains that just
make you hotUseful gains Useful
10 Definition: Interaction Factor
• Interaction Factor = Thermal Coupling• HPWHs are a negative internal gain• HCƒ – heating and cooling interaction factor (0% - 100%)
– What fraction of the maximum possible interaction is “seen” by the HVAC system?
– Primary hypothesis for the value being less than 100%: • HPWH is located in a space that’s somewhat coupled to the outside• HPWH extracts heat and sometimes that heat comes directly from outside
• How much of the heat removed by the HPWH is realized as an internal gain/loss?
• Note: HCƒ differs from thermal utility which remains nearly unchanged regardless of a HPWHs thermal coupling
House Heating Loads and Gains
QLoad = UAΔT – QIntGains – Qsolar
QIntGains = QHeatGains + QHPWH
QHeatGains = QRefrig + QTV + QWii + QLights + …
0 2 4 6 8 10 12 14 16 18 20 22 24
UAΔT
QHeatGains
Hour of Day
QLo
ad
Qsolar
Symmetry in Positive and Negative Gains
QLoad = UAΔT – QIntGains – Qsolar
QIntGains = QHeatGains + QHPWH
QHeatGains = QRefrig + QTV + QWii + QLights + …
0 2 4 6 8 10 12 14 16 18 20 22 24
UAΔT
QHeatGains
Qsolar+1kW
-1kW
Hour of Day
QLo
ad
IntGain,i(+) = Decreased thermal load on HVAC from increased internal gains [kWh/day]
IntGain,i(-) = Increased thermal load on HVAC from decreased internal gains [kWh/day]
IntGain,i(+) = IntGain,i(-)
QIntGain,+ = (-1) * QIntGain,-
Thermal Utility Complications in Measuring Thermal Coupling
If thermal utility is not constant:• thermal coupling can’t be measured• positive and negative gains are not
symmetric.
0 2 4 6 8 10 12 14 16 18 20 22 24
UAΔT
QHeatGains
Qsolar
January
March
+1kW
-1kW
Hour of Day
QLo
ad
House floats off set point and the +1kW internal gains are no longer useful – their thermal utility changed. Moreover, the change in areas between the dashed March line and the red and blue lines is now different – the gains don’t have a symmetric utility
Doh!
Complications: A More Nuanced View
0 2 4 6 8 10 12 14 16 18 20 22 24
UAΔT
QHeatGains
Qsolar
March
+1kW
-1kW
Hour of Day
QLo
ad
Tin
• House floats off set point. Load changes. Heat loss increases over that time period. Drywall stores heat. Sun goes away. Some, but not all heat returned to house as it “coasts” back to set point.
TSet Point
Qsolar
Controlling for Thermal Utility Complications Via Experimental Design
QLoad = UAΔT – QIntGains – Qsolar
QIntGains = QHeatGains + QHPWH
QHeatGains = QRefrig + QTV + QWii + QLights + …
QHPWH = QUAtank + Qcompressor (Qcompressor is negative)
0 2 4 6 8 10 12 14 16 18 20 22 24
UAΔT
QHeatGains
Test when the load is high
+1kW
-1kW
Hour of Day
QLo
ad
IntGain,i(+) = Decreased thermal load on HVAC from increased internal gains [kWh/day]
IntGain,i(-) = Increased thermal load on HVAC from decreased internal gains [kWh/day]
IntGain,i(+) = IntGain,i(-)
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Equipment to Induce Temp Effect
What equipment should be used to induce the localized temperature change in the experiment home?
CAT Proposal: space heater• Least uncertainty in thermal output• Easiest and cheapest to implement• Produces symmetric HVAC effect if studied under the proper
conditions• A generic load that can represent other measures that interact with HVAC equipment
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Question 2
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What locations and conditions should be tested in the experiment home?
• Example Locations: BDRM-2, Master bath closet, near thermostat• Example Conditions: door open or closed (if applicable), central/zonal heat
Locations/Conditions of Test Cases
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Locations/Conditions of Test Cases (cont’d)
• Each test case will be run for a period of 5-10 days• A minimum outdoor air temperature during test period should be
required in order to ensure symmetry effect• Test cases should represent a wide range of a space’s
“connectedness” to the thermostat– E.g. space near thermostat should be highly connected– Spaces far away and/or highly buffered from thermostat will likely be less connected
• Test cases should be generic and test the expected range of HVAC interaction factors to the extent possible– E.g. a test case in the living room near the thermostat does not suggest HPWHs being installed in
a living room, but rather attempts to place a “book end” on the factor of interest– Not all cases can be directly tested, e.g. a heated basement
• CAT proposes a phased approach to the research– First phase serves as proof of concept and may be sufficient on its own– Additional phases could be added to study additional scenarios– Additional reasons to phase research: peak season is only so long, other
competing projects for PNNL Lab Homes
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Test Case Proposal
Test Case Description Test Location (on Floorplan)
Door Open or Closed?
Purpose of / Reason to Include Test Case
Water Heater Closet A N/A May be most disconnected area from the thermostatUtility Closet B N/A Most connected to the return ductLiving Room C N/A Probably the most connected area to the thermostatMaster Bath, Door Open D Open Highly buffered/disconnected from the thermostatMaster Bath, Door Closed D Closed Even more buffered from the thermostat
AB
CD
CAT recommends all test cases use the same HVAC system (central) for first phase of research.
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Test Case Proposal
• Thoughts from the subcommittee? • Does the subcommittee support this
proposal?
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Subcommittee Recommendation
1. What equipment should be used to induce the localized temperature change in the experiment home?
Subcommittee recommendation:
2. What locations and conditions should be tested in the experimental home?
Subcommittee recommendation: